As far as I know stages and boosters are cylndircal up to now and I suppose that this is due to aerodynamics.

Now the CXV won't be cylindrical but washtub-shaped for reentry as one measure to achieve reusability.

What about the idea of stages and boosters which can reshape for reentry and which are equipped by a cooling system like that of the CXV? They would be reusable that way I think.

Regarding stages and booster which are used for interplanetary flights - if they would return to orbit they could be made reusable easyly. What about making them spherical instead of cylindrical in that case? Are there arguments against spherical stages that never would reenter? They would have the advantage of requiring a minimized amount of material and thus investment.

As far as I know stages and boosters are cylndircal up to now and I suppose that this is due to aerodynamics.

You got it.

Ekkehard Augustin wrote:

Now the CXV won't be cylindrical but washtub-shaped for reentry as one measure to achieve reusability.

Also due to aerodyamics. The actual vehicles (as opposed to the rocket, or "stack") tend to be non-cylindrical, so they are easily controllable on reentry.

Ekkehard Augustin wrote:

What about the idea of stages and boosters which can reshape for reentry and which are equipped by a cooling system like that of the CXV? They would be reusable that way I think.

Yup, but you wouldn't have any room for the fuel or the engines, what with all the equipment you'd need to implement a variable-geometry structure (something that changes shape) at the insane speeds that a returning orbiter experiences, and keep it sturdy enough not to disintegrate.

Ekkehard Augustin wrote:

Regarding stages and booster which are used for interplanetary flights - if they would return to orbit they could be made reusable easyly. What about making them spherical instead of cylindrical in that case? Are there arguments against spherical stages that never would reenter? They would have the advantage of requiring a minimized amount of material and thus investment.

Once something is consigned to stay in space permanently, you open up whole new worlds of design possibilities. The trick lies in getting all this stuff to orbit in the first place, which is why most current satellites are still roughly cylindrical -- that's the easiest shape to put on top of a stack. Otherwise, you incur brand-new weight penalties by having to fair the thing into the rocket that's launching it.

If spherical tanks used during alaunch from ground to orbit can be reused for launches from the orbit to HEO, GEO or interplanetary destinies this is a kind of reusability which has significant potentials to reduce costs.

Several spherical tanks could be placed in orbit for later use this way and perhaps scalability could be achieved by having available several small spherical tanks instead of one large only. But several spherical tanks instead of one only could mean suboptimal investment costs.

The segments of a larger spherical tank could be put together at an orbital assembly yard - what about that?

Could such a tank be inflatable like Bigelow's Nautilus? Is it possible to avoid the problems of reshapable tanks then?

It would be sufficient, if the tanks would be approximately spherical only - they could be made of several hexagons for example.

One of the important things to understand is the need to separate boosters safely. If you look at pages 56-59 of the Oct. 24, 2005 issue of AW&ST, you will see, for example, how the second stage engine of the AirLaunch rocket is submerged in the inside the first stages propane fuel tank!

"For stage separation, Quick Reach I is to have a pyrotechnic cord sever the first stage tank wall 2 ft. below where it transitions to the second stage tank wall....The submerged upper-stage engine is a clever idea used in the Russian R-27/SS-N-6 submarine-launched ballistic missile, which is also pressed to fit in a small space."